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It might be a blazed grating. Have you checked to see whether it's truly diffracting only to one side, or whether it is simply diffracting most of its energy in that direction? Are you using it as a transmissive grating, or as a reflective grating?

Bringing this back from the dead. I actually study crossed diffraction, or diffraction from multiple gratings. What I can say as of now is that each grating separates the beam into different orders. For my case, I have multiple gratings arranged side by side, and the output is a collection of beams that is made up of the individual components of each beam. The diffraction occurs at the direction perpendicular to the grating, so each of the grating orientations diffracts the beam in a perpendicular direction. What you see there is the first beam going through one grating, and then the 0th order and diffracted orders from the first grating hit the second and diffract in a direction perpendicular to grating 2, so you get cross like patterns.

Since this topic is already back from the dead..
Anyone happen to calculate the lines per mm/in on PHR-803T or any sled diffraction grating?
Or perhaps someone would kindly give an example for calculating lines per mm given a wavelength of 532nm & distance of 5 or 10 ft?
I'm afraid I've been out of school too long to use the formula without help.

Since this topic is already back from the dead..
Anyone happen to calculate the lines per mm/in on PHR-803T or any sled diffraction grating?
Or perhaps someone would kindly give an example for calculating lines per mm given a wavelength of 532nm & distance of 5 or 10 ft?
I'm afraid I've been out of school too long to use the formula without help.

you can use the grating equation to calculate that, specifically, the grating period. I am guessing that it is going to be around 5-10 um for the gratings in these sleds, but to calculate it, you need to use this formula:

(1) m*lambda/d=sin(thetai)+sin(thetad)

For simplicity, do it at normal incidence, so sin(thetai) disappears, and you can solve for d, if you know the wavelength lambda of the laser and the order and the diffraction angle:

(2) d=m*lambda/sin(thetad)

You can get theta d by knowing the distance from the grating to your "screen" (call this "a"), and the distance from the 0th order or center beam to the diffracted order (call this "b"). To get the angle, which is the diffraction angle for that particular order (remember to take order into account), use the trig relationship tan(thetad)=b/a, or:

(3) thetad=arctan(b/a)

Substitute (3) into (2) to get the grating spacing d. Keep everything in meters for now (wavelength and spacing, a and b).